Mesh-restorable networks with enhanced dual-failure restorability properties

We consider extensions of the most common mesh-restorable network capacity design formulation that enhance the dual-failure restorability of the designs. A significant finding is that while design for complete dual-failure restorability can require up to triple the spare capacity, dual failure restorability can be provided for a fairly large set of priority paths with little or no more spare capacity than required for single-failure restorability. As a reference case we first study the capacity needs under complete dual-failure restorability. This shows extremely high spare capacity penalties. A second design model allows a user to specify a total capacity (or budget) limit and obtain the highest average dual-failure restorability possible for that investment limit. This formulation, and a relationship between dual-failure restorability and availability, can be used to trace-out the capacity-versus-availability trade-off curve for a mesh network. A third design strategy supports multiple-restorability service class definitions ranging from best-efforts-only to an assurance of complete single and diud-failure restorability on a per-demand basis. This lets a network operator tailor the investment in protection capacity to provide ultra-high availability on a service-selective basis, while avoiding the very high investment that would be required to support complete dual-failure restorability of the network as a whole.